<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /*（4）第四种还是利用绝对定位的方式，将父级元素设置为相对定位。左边元素宽度设置为200px，右边元素设置为绝对定位，左边定位为200px，其余方向定位为0。*/
    .router {
      position: relative;
      height: 100px;
    }

    .left {
      width: 200px;
      height: 100px;
      background-color: tomato
    }

    .right {
      position: absolute;
      left:200px;
      top:0;
      bottom:0;
      right:0;
      background-color: gold
    }
  </style>
</head>

<body>
  <div class="router">
    <div class="left">left200px</div>
    <div class="right">right自适应</div>
  </div>
</body>

</html>